Under Armour plans to hire hundreds of workers at its Locust Point headquarters this year, expand facilities on its campus and bring its brand of sports apparel and footwear to new markets in the U.S. and around the world.

CEO Kevin Plank outlined the goals Tuesday while promising shareholders more of the rapid growth that has defined the $1.8 billion company in recent years.

During an annual meeting in which Under Armour pitchman and record-setting Olympic swimmer Michael Phelps made a surprise appearance, Plank said the company is just beginning to make inroads in areas such as athletic footwear, women's sports apparel and international markets, with room to grow.

"We are a growth company," Plank said. "We were a compression T-shirt company, and today we are so much more than that."

Plank said the company's success means more jobs for Baltimore. Nearly 1,500 of Under Armour's 6,000 worldwide employees work at the Locust Point headquarters. An additional 300 employees will be hired at the campus this year, he said.

Much of Under Armour's growth, Plank said, will depend upon the company's ability to create innovative products that solve problems for athletes and to develop new distribution channels, such as Under Armour branded stores. The company opened an Under Armour Brand House store in Harbor East in February.

The company is also growing internationally. Last year, Under Armour opened three new stores in China, with more planned, and saw rapid growth in sales in Japan.

Plank noted that the compression T-shirts and other compression products accounted for well over half of the company's sales in 2005 when it went public. But that category now only accounts for 14 percent of total sales, as Under Armour has developed new apparel, including a line of products designed to keep athletes warm in extreme conditions that will be introduced this fall.

The men's apparel category, which accounted for the biggest share of sales for Under Armour last year, remains highly competitive, Plank said. But the company has seen success with its new line of "Alter Ego" superhero shirts, created with D.C. Comics and Marvel Comics.

"It's been the most talked-about thing at retail," Plank said. "We cannot keep it in the stores."

Tuesday's meeting came with a surprise for some of the 250 shareholders in attendance: an appearance by Phelps, who has had an endorsement deal with Under Armour since 2010 and was on the campus Tuesday for a photo shoot.

The company is known for jazzing up annual meetings with attention-grabbing videos showcasing products and by introducing Under Armour athletes. Plank broke from his prepared remarks to say the crowd might want to hear from one of them.

"Is Michael Phelps in the house?" Plank asked, as shareholders looked around in anticipation.

Phelps, wearing gray pants, a black shirt and yellow athletic shoes — all displaying the Under Armour logo — slipped into the Cheer Building's "arena" from behind a black curtain and sat on a stool next to Plank.

The chatter between the two quickly turned to playing golf. The swimmer has been appearing in the Golf Channel reality program "The Haney Project," where a former coach of Tiger Woods' works with celebrities to help them improve their game. Phelps said the show has allowed him to play some of the best courses in the world over the past six months and travel to locales such as Scotland and the Bahamas.

"My swing is so much better," he said. "When I started the game of golf, I said, 'This can't be that hard.'"

But he learned otherwise.

"It takes a lot time and a lot of hard work," he said. "The worst thing was my hands, taping up my hands" to prevent blisters.

Phelps' golfing experience has also meant a foray into unfamiliar territory, such as one competition where his missed shots prompted booing from the fans.

Phelps said he's been back in the water a couple of times but has not reconsidered his decision to retire from competitive swimming.